package pack0619;

public class DemoF {
    public static void main(String[] args){
        int a=0;
        int b=1;
        int x;
        int sum=0;
        for (int i=1;i<=20;i++){
            x=a+b;
            a=b;
            b=x;
            sum=sum+x;
        }
        System.out.println(sum);
    }
}
